1. Technical Field
The present invention relates to networks of devices that can be connected using wireless links, in particular devices that use the Bluetooth technology. Specifically, embodiments of the present invention pertain to a method and system for selecting and connecting to wireless access point within a local area network.
2. Background Art
One prevalent technology for wireless distribution of audio and data is Bluetooth, where its popularity is based on it providing a high-performance, yet low-cost, integrated radio transceiver. Bluetooth protocol is known in the art as a short range (10 meter) frequency-hopping radio link between devices. These devices are then termed “Bluetooth-enabled”. Bluetooth is a trademark owned by Bluetooth SIG, Inc. Bluetooth technology allows Bluetooth devices to “discover” other Bluetooth devices that are within range and then connect with those devices, either automatically or at a user's discretion.
Prior art FIG. 1 depicts a wireless microphone 11 that is sending audio, via a Bluetooth RF communication link 100, to a wireless audio access point 18 that is configured as a wireless communication access point. This application is suitable for a teacher, using this wireless microphone 11, to address students in a classroom setting. Such audio distribution using Bluetooth is well understood in the prior art and is similar to Bluetooth links between mobile telephones and microphone headsets, etc.
Bluetooth radios operate in the ISM (Industrial, Scientific, and Medical) band at 2.4 GHz (gigahertz). A frequency hop transceiver is applied to combat interference and fading. Bluetooth uses a packet-switching protocol based on a frequency hop scheme with 1600 hops/second. Slots can be reserved for synchronous packets. A packet nominally covers a single slot, but can be extended to cover up to five slots. Each packet is transmitted in a different hop frequency. The entire available frequency spectrum is used with 79 hops of one (1) MHz (megahertz) bandwidth, defined analogous to the IEEE (Institute of Electronic and Electrical Engineers) 802.11 standard.
A connection between devices is made by a page message if the address is already known, or by an inquiry message followed by a page message if the address is unknown. The inquiry message enables the Bluetooth device to discover which other Bluetooth units are in range and what their addresses are, as well as other information such as their clocks and class-of-device. A “discoverable device” is a Bluetooth device in range that will respond to an inquiry (normally in addition to responding to a page). A discoverable device scans for inquiry messages, referred to as “inquiry scan.” A “connectable device” is a Bluetooth device in range that will respond to a page.
Bluetooth communication is established first by having an unconnected Bluetooth (initiator) device broadcast an ‘Inquiry’ command that instructs all other Bluetooth devices in the immediate vicinity that are ‘discoverable’, to provide their respective Bluetooth addresses and clock values. Accordingly, the wireless microphone 11 broadcasts a Bluetooth inquiry 101 and the wireless audio access point 18 responds by broadcasting a Bluetooth inquiry response 102. Although not illustrated, those skilled in the art will appreciate that all other discoverable Bluetooth devices in the immediate vicinity will also broadcast their own Bluetooth inquiry responses.
Next, the still unconnected wireless microphone 11 pages each of the discovered Bluetooth devices and, based on contents of their responses, determines to which other Bluetooth device it desires to connect. A Bluetooth ‘Master page response’ is then sent to the desired device and the desired device accepts the connection. In this example, the wireless audio access point 18 is the desired device to which the wireless microphone 11 will attempt to connect. To complete this Bluetooth connection example, the final step is for the wireless audio access point 18 to take control of the Bluetooth link by becoming the ‘master’ and causing the wireless microphone 11 to become the ‘slave’. This transfer of control is accomplished using a Bluetooth ‘LMP_switch_req’ command. The above described example of establishing a Bluetooth communication link is detailed further in Table 1.
TABLE 1AccessPacketHoppingCodeStepMessageTypeDirectionSequenceand Clock-- Discover Bluetooth Devices --a.1InquiryIDMaster toInquiryInquiryslavea.2Inquiry responseFHSSlave toInquiryInquiry(A)masterresponse..................a.2Inquiry responseFHSSlave toInquiryInquiry(N)masterresponse-- Connect to Desired Device and Switch Roles (Master/Slave) --b.1PageIDMaster toPageSlaveslaveb.2First slave pageIDSlave toPageSlaveresponsemasterresponseb.3Master pageFHSMaster toPageSlaveresponseslaveb.4Second slaveIDSlave toPageSlavepage responsemasterresponseb.51st packetPOLLMaster toChannelMastermasterslaveb.6LMP_slot_offsetDM1/Slave toChannelMasterDVmasterb.7LMP_switch_reqDM1/Slave toChannelMasterDVmasterb.8LMP_acceptedDM1/Master toChannelMaster*DVslave*After “LMP_accepted” message, the previous slave is now master and vice versa.
One drawback of the prior art is that the wireless audio access point 18 must always, or least periodically, be discoverable in order to establish a new link with a previously unconnected wireless microphone 11. In an alternative way of establishing a Bluetooth link, the wireless audio access point 18 issues the Bluetooth ‘inquiry’, either periodically to search for new devices or by a manual operator action. This alternative suffers from the drawback of either having to reserve Bluetooth bandwidth for the periodic search or of requiring a manual operator action at the wireless audio access point 18. In addition, both prior art alternatives will allow the devices to be discovered by extraneous Bluetooth devices outside of the audio system and also allow the audio system to discover these extraneous devices. Examples of such extraneous devices include, but are not limited to: cell phones and associated earpieces, desktop and laptop computers, fax machines, game controllers, keyboards and mice, personal digital assistants (PDA), and printers.
Table 2 below lists the ranges associated with the various classes of Bluetooth radios.
TABLE 2Maximum PermittedPower mWRangeClass(dBm)(approximate)Class 1100mW (20 dBm)~100metersClass 22.5mW (4 dBm)~10meters*Class 31mW (0 dBm)~1meter*In most cases the effective range of class 2 devices is extended if they connect to a class 1 transceiver, compared to a pure class 2 network. This is accomplished by the higher sensitivity and transmission power of Class 1 devices.
FIG. 2 depicts a portion of a school building having several classrooms and with the wireless range of a typical Bluetooth device thereupon superimposed. This clearly shows that in a typical school setting, the range of a class 2 Bluetooth device 210, such as wireless audio access point 18, located in a first classroom 21 extends well beyond the confines of that classroom. As shown, the wireless audio access point 18 located in the first classroom 21 would interact, such as by trying to establish the Bluetooth RF communication link 100, with any Bluetooth devices located in a second classroom 22, a fourth classroom 24, and a fifth classroom 25. The Bluetooth wireless audio access point 18 also interacts with some portion of the Bluetooth devices in a third classroom 23, a sixth classroom 26, a seventh classroom 27, and an eighth classroom 28. In fact, in the typical school layout illustrated only devices in a ninth classroom 29 would not interact with the Bluetooth wireless audio access point 18 in the first classroom 21, but even that is not assured, as described above in the table notes for Table 2.
Prior art FIG. 3 depicts a portable wireless device communicating with a wireless communication access point using Bluetooth and additionally including IrDA, an infrared digital protocol, in order to accelerate Bluetooth connection times in accordance with a known method. For example, the Bluetooth Specification provides for an out of band (OoB) association to discover the devices as well as to exchange or transfer cryptographic numbers used in the pairing process.
As shown in FIG. 3, a portable wireless device may include both a Bluetooth radio and an Infrared Data Association (IrDA) high speed infrared protocol. An IrDA communication link 300 is a low power infrared (IR) signal having high-speed characteristics (i.e. baud rate of 9600 baud or greater) and short range (i.e. limited to 1 meter). Portable wireless device 31 includes both a Bluetooth RF antenna 311 and an IrDA infrared transceiver 313. Similarly, wireless communication access point 38 also includes both a corresponding Bluetooth RF antenna 381 and a corresponding IrDA infrared transceiver 383.
Now, the prior art simply does not provide an effective means of limiting Bluetooth communications to the confines of a single classroom. Although the prior does include certain provisions for out of band (OoB) communications, including IrDA, these provisions are not suitable for a classroom audio system where communication between a wireless microphone and a wireless audio access point is based on collocation within the confines of the same classroom.
Thus, attempting to use an existing Bluetooth wireless microphone device in a multiple classroom setting, where each classroom potential has its own wireless audio access point, presents a number of problems. Finding a solution to these problems is made more complex because the solution must be substantially compliant with the Bluetooth specification and also be low power.